U.S. patent number 6,297,326 [Application Number 08/733,551] was granted by the patent office on 2001-10-02 for grafted polyolefin compositions.
This patent grant is currently assigned to Kimberly-Clark Corporation. Invention is credited to David Michael Schertz, James Hongxue Wang.
United States Patent |
6,297,326 |
Wang , et al. |
October 2, 2001 |
Grafted polyolefin compositions
Abstract
A polyolefin, such as polyethylene or polypropylene, is modified
by grafting onto the polyolefin backbone from 5 weight percent to
about 30 weight percent of 2-hydroxyethyl methacrylate. Suitable
polyethylene compositions for grafting include ultra high molecular
weight polyethylene, high density polyethylene, ultra low density
polyethylene, low density polyethylene, linear low density
polyethylene and polypropylene.
Inventors: |
Wang; James Hongxue (Appleton,
WI), Schertz; David Michael (Appleton, WI) |
Assignee: |
Kimberly-Clark Corporation
(Neenah, WI)
|
Family
ID: |
24948095 |
Appl.
No.: |
08/733,551 |
Filed: |
October 18, 1996 |
Current U.S.
Class: |
525/303; 525/242;
525/309; 525/69 |
Current CPC
Class: |
C08F
255/00 (20130101); C08F 255/00 (20130101); C08F
220/20 (20130101) |
Current International
Class: |
C08F
255/00 (20060101); C08L 023/26 (); C08F
255/02 () |
Field of
Search: |
;525/303,309,242,69 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0562582 |
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1393693 |
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2 295 553 A |
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49-126742 |
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61-272217 |
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Other References
Bartczak, Z. and A. Galeski, "Changes in Interface Shape During
Crystallization in Two-Component Polymer Systems," Polymer, 1986,
vol. 27, Apr., pp. 544-548. .
Mortensen, Kell, "Phase Behavior of Poly(propylene
Oxide)-Poly(ethylene oxide)-Poly(propylene oxide) Triblock
Copolymer Melt and Aqueous Solutions," Macromolecules, vol. 27, No.
20, 1994, pp. 5654-5666. .
Song, Z. and W. E. Baker, "Melt Grafting of T-Butylaminoethyl
Methacrylate Onto Polyethylene," Polymer, 1992, vol. 33, No. 15,
pp. 3266-3273. .
Tang, Tao and Baotong Huang, "Compatibilization of
Polypropylene/Poly (Ethylene Oxide) Blends and Crystallization
Behavior of the Blends," Journal of Polymer Science: Part B:
Polymer Physics, vol. 32, (1994), pp. 1991-1998..
|
Primary Examiner: Mullis; Jeffrey
Attorney, Agent or Firm: Kilpatrick Stockton LLP
Claims
What is claimed is:
1. A modified polyolefin composition comprising from about 70
weight percent to 90 weight percent of a polyolefin homopolymer and
from greater than 10 weight percent to about 30 weight percent of
2-hydroxyethyl methacrylate grafted to said polyolefin homopolymer,
wherein said modified polyolefin composition is made by the process
of
a) contemporaneously adding to an extruder an amount of the
polyolefin homopolymer, an amount of 2-hydroxyethyl methacrylate
and an amount of a free radical initiator to a reaction vessel,
wherein the amount of the 2-hydroxyethyl methacrylate relative to
the amount of polyolefin homopolymer is a ratio of 0.1 to about 0.2
and the amount of free radical initiator relative to the amount of
2-hydroxyethyl methacrylate is a ratio from about 0.025 to about
0.1, wherein said amounts base based on weight, further wherein the
polyolefin has a number average molecular weight of greater than
about 40,000 g/mol; and
b) mixing the constituents of (a) under appropriate conditions to
melt graft 2-hydroxyethyl methacrylate onto the polyolefin at a
grafting efficiency of at least 50 percent;
wherein the modified polyolefin composition is substantially
soluble in xylenes, and wherein the modified polyolefin composition
is capable of being used in thermoplastic film-forming
applications.
2. The modified polyolefin composition of claim 1 wherein the free
radical initiator is selected from the group consisting of benzoyl
peroxide; di-t-butyl peroxide; dicumyl peroxide; cumyl butyl
peroxide; 1,1-di-t-butyl peroxy-3,5,5-trimethylcyclohexane;
2,5-dimethyl-2,5-di(t-butylperoxy) hexane; 2,5-dimethyl-2,5-bis
(t-butylperoxy) hexyne-3; bis(a-t-butyl peroxyisopropylbenzene);
t-butyl peroxypivalate; t-butyl peroctoate; t-butyl perbenzoate;
2,5-dimethylhexyl-2,5-di(perbenzoate); t-butyl di(perphthalate);
t-butyl hydroperoxide; p-methane hydroperoxide; pinane
hydroperoxide; cumene hydroperoxide; cyclohexanone peroxide and
methyl ethyl ketone peroxide.
3. The modified polyolefin composition of claim 1, wherein said
polyolefin homopolymer is selected from the group consisting of
ultrahigh molecular weight polyethylene, high density polyethylene,
ultra low density polyethylene, low density polyethylene, linear
low density polyethylene, polypropylene, and mixtures thereof.
4. The modified polyolefin composition of claim 1, wherein said
polyolefin homopolymer has a melt index greater than about 0.01
dg/min. to about 100 dg/min. at 2.16 kg and 190.degree. C.
5. The modified polyolefin composition of claim 1, wherein said
polyolefin homopolymer has a melt index of about 0.05 dg/min. to
about 25 dg/min. at 2.16 kg and 190.degree. C.
6. The modified polyolefin composition of claim 1, wherein the
2-hydroxyethyl methacrylate is present in an amount of from about
10 to about 25 weight percent.
7. The modified polyolefin composition of claim 1, wherein the
2-hydroxyethyl methacrylate is present in an amount of from about
10 to about 20 weight percent.
Description
BACKGROUND OF THE INVENTION
The present invention relates to graft copolymers of polyolefins
and alkyl acrylate and processes for preparing the copolymers. More
particularly, the invention relates to melt grafting 2-hydroxyethyl
methacrylate onto polyethylene and polypropylene resins and a
process for preparing such polymers.
Polyolefins such as polyethylene and polypropylene are non-polar
polymers that, in general, are resistant to polar moieties. These
polyolefins are customarily used commercially for barrier film
applications. Such applications include product packaging to such
commodities as disposable personal products like, sanitary napkins,
diapers, adult incontinence products and the like.
Used polymers are typically disposed of by recycling, incineration
or land filling. Because of the increasing amount of material being
sent to landfills it is becoming more important for the refuse to
be biodegradable, compostable or both. In the area of disposable
personal products, the outer polyethylene film layer has to be
separated from the rest of the absorbent structure or the entire
structure has to be comminuted.
Over the past decade or so interest has grown in modifying existing
polymers to achieve commercially important copolymers having
improved and, at times, specific properties. This has been
particularly evident in the drive to modify commodity polymers such
as polyolefins with polar functional monomers such as acrylic acid
and alkyl acrylates. For example, linear low-density polyethylene
has been modified by melt grafting up to about 5 weight percent
(wt. %) t-butylaminoethyl methacrylate (t-BAEMA) to produce a
copolymer having improved properties for co-extrusion as tie
layers. These tie layers are commercially important in the
packaging and film industry to economically produce packages
meeting specific requirements and sometimes governmental
regulations.
Polyolefins have also been modified using acrylate esters such as
methyl acrylate, 2-butyl acrylate, 2-ethylhexyl acrylate, decyl
acrylate, octadecyl acrylate and corresponding esters of
methacrylate.
Moreover, there is an increased emphasis on environmentally safe
coatings for plastics. These coatings are reducing the use of
solvent based coatings and relying, to an ever increasing degree,
on polar coatings such as water based materials. The utility of the
graft copolymer of the present invention includes, but would not be
limited to, materials having a greater affinity for a polar
coating. Other uses may include wire coatings, injected molded
articles and barrier films having increased mechanical
compatibility between the graft copolymer of the present invention
and hydrophilic compositions.
The production of the compositions has generally been accomplished
by blending all the constituents into a monomer-coated resin
mixture. The heterogeneous mixture of resin coated with monomer is
then extruded, in the presence of a reaction initiator, to form a
graft copolymer. This method has been successful to produce graft
copolymers having a comparatively low weight percent of grafted
monomer. Moreover, the efficiency of grafted monomer to the
polyolefin resin is low, with an efficiency of less than 50
percent. Due to the grafting limitations and process inefficiency,
there is a need for graft copolymers having a greater amount of
monomer grafted to the polyolefin and an efficient process that is
capable of producing such copolymers.
SUMMARY OF THE INVENTION
Briefly, the present invention is a modified polyolefin copolymer
having from 95 weight percent to about 70 weight percent of a
polyolefin with the remaining portion of the composition an alkyl
acrylate monomer grafted thereto, wherein the percent grafted
monomer is based on the weight of the polyolefin and the weight of
the grafted (meth)acrylate. More specifically, the composition of
the present invention is an ethylene or propylene polymer
composition having from 95 weight percent to about 70 weight
percent of the polyolefin and from 5 weight percent to about 30
weight percent of 2-hydroxyethyl methacrylate (HEMA) monomer
grafted thereto. As used herein 2-hydroxyethyl methacrylate and
HEMA are the same compound.
Surprisingly, it has now been found that graft copolymers of
polyethylene or polypropylene can be obtained by melt grafting high
levels, 5 weight percent to about 30 weight percent, of
2-hydroxyethyl methacrylate onto the polyolefin backbone.
Another aspect of the invention is a method of making the graft
copolymer described herein. The polyolefin copolymer of this
invention can be made by adding to a suitable reaction vessel and
under melt grafting conditions, a predetermined amount of
polyolefin polymer, adding a predetermined amount of 2-hydroxyethyl
methacrylate monomer and a sufficient amount of reaction initiator
to the melt to graft from 5 weight percent to about 30 weight
percent of the 2-hydroxyethyl methacrylate onto the polyolefin.
Desirably, the polyolefin copolymer is cooled sufficiently to
solidify the melt
It is a general object of the invention to provide a composition
having a higher weight percent of grafted monomer to a polyolefin
than previously known. A more specific object of the invention is
to provide a graft copolymer polyolefin having greater than 5
weight percent monomer grafted thereto.
Another object of the invention is to provide a composition having
from 95 weight percent to about 70 weight percent of polyethylene
and from 5 weight percent to about 30 weight percent 2-hydroxyethyl
methacrylate grafted thereto.
Another object of the invention is to provide a composition having
from 95 weight percent to about 70 weight percent of polypropylene
and from 5 weight percent to about 30 weight percent 2-hydroxyethyl
methacrylate grafted thereto.
It is another object of the invention to provide a method of melt
grafting 2-hydroxyethyl methacrylate onto a polyolefin resin under
melt conditions.
DETAILED DESCRIPTION OF THE INVENTION
The saturated ethylene polymers useful in the practice of this
invention are homopolymers or copolymer of ethylene and
polypropylene and are essentially linear in structure. As used
herein, the term "saturated" refers to polymers which are fully
saturated, but also includes polymers containing up to about 5%
unsaturation. The homopolymers of ethylene include those prepared
under either low pressure, i.e., linear low density or high density
polyethylene, or high pressure, i.e., branched or low density
polyethylene. The high density polyethylenes are generally
characterized by a density that is about equal to or greater than
0.94 grams per cubic centimeter (g/cc). Generally, the high density
polyethylenes useful as the base resin in the present invention has
a density ranging from about 0.94 g/cc to about 0.97 g/cc. The
polyethylenes can have a melt index, as measured at 2.16 kg and
190.degree. C., ranging from about 0.005 decigrams per minute
(dg/min) to 100 dg/min. Desirably, the polyethylene has a melt
index of 0.01 dg/min to about 50 dg/min and more desirably of 0.05
dg/min to about 25 dg/min. Alternatively, mixtures of polyethylene
can be used as the base resin in producing the graft copolymer
compositions, and such mixtures can have a melt index greater than
0.005 dg/min to less than about 100 dg/min.
The low density polyethylene has a density of less than 0.94 g/cc
and are usually in the range of 0.91 g/cc to about 0.93 g/cc. The
low density polyethylene polymer has a melt index ranging from
about 0.05 dg/min to about 100 dg/min and desirably from 0.05
dg/min to about 20 dg/min. Ultra low density polyethylene can be
used in accordance with the present invention. Generally, ultra low
density polyethylene has a density of less than 0.90g/cc.
Generally, polypropylene has a semi-crystalline structure having a
molecular weight of about 40,000 or more, a density of about 0.90
g/cc, a melting point of 168 to 171.degree. C. for isotactic
polypropylene and a tensile strength of 5000 psi. Polypropylene can
also have other tacticities including syndiotactic and atactic.
Copolymers of ethylene which can be useful in the present invention
may include copolymers of ethylene with one or more additional
polymerizable, unsaturated monomers. Examples of such copolymers
include, but are not limited to, copolymers of ethylene and alpha
olefins (such as propylene, butene, hexene or octene) including
linear low density polyethylene, copolymers of ethylene and vinyl
esters of linear or branched carboxylic acids having 1-24 carbon
atoms such as ethylene-vinyl acetate copolymers, and copolymers of
ethylene and acrylic or methacrylic esters of linear, branched or
cyclic alkanoes having 1-28 carbon atoms. Examples of these latter
copolymers include ethylene-alkyl (meth)acrylate copolymers, such
as ethylene-methyl acrylate copolymers.
The free radical initiators useful in the practice of this
invention include acyl peroxides such as benzoyl peroxide; dialkyl;
diaryl; or aralkyl peroxides such as di-t-butyl peroxide; dicumyl
peroxide; cumyl butyl peroxide; 1,1-di-t-butyl
peroxy-3,5,5trimethylcyclohexane;
2,5-dimethyl-2,5-di(t-butylperoxy) hexane; 2,5-dimethyl-2,5bis
(t-butylperoxy) hexyne-3 and bis(a-t-butyl peroxyisopropylbenzene);
peroxyesters such as t-butyl peroxypivalate; t-butyl peroctoate;
t-butyl perbenzoate; 2,5-dimethylhexyl-2,5di(perbenzoate); t-butyl
di(perphthalate); dialkyl peroxymonocarbonates and
peroxydicarbonates; hydroperoxides such as t-butyl hydroperoxidle,
p-methane hydroperoxide, pinane hydroperoxide and cumene
hydroperoxide and ketone peroxides such as cyclohexanone peroxide
and methyl ethyl ketone peroxide. Azo compounds such as
azobisisobutyronitrile may also be used.
Other components well known in the art can be added to the graft
copolymers to further enhance the properties of the resulting
material. For example, polyethylene glycol can be added to improve
the melt viscosity. Additives of other types normally used in
polymer blends can also be incorporated to provide specific
properties as needed. For example, anti-static agents, pigments,
colorants and the like. Additionally, processing characteristics
can be improved by incorporating lubricants or slip agents into the
blends. All of these additives are generally used in relatively
small amounts, usually less than 3 weight percent.
Another aspect of the invention is a method for making the
compound. Generally, at low levels of grafting, usually less than 3
weight percent of the monomer the method is not especially
critical, and can be practiced by mixing the desired weight ratio
of the polyolefin and 2-hydroxyethyl methacrylate in a blend vessel
prior to melt milling or grafting. At greater than bout 3 weight
percent grafting, the 2-hydroxyethyl methacrylate is mixed with the
polyolefin polymer at a temperature above the softening point or
above the temperature where they undergo deformation and are
converted to a molten or fluid state.
The mixture of polyolefin and 2-hydroxyethyl methacrylate are
subjected to mechanical deformation in a suitable mixing device,
such as a Brabender Plasticorder, a roll mill, a single or multiple
screw extruder or any other of the well known mechanical mixing
equipment normally used in the mixing, compounding, processing or
fabrication of polymers. A particularly desirable reaction vessel
is an extruder having one or more ports.
The solid polyolefin, e.g., pellets or powder may be
contemporaneously added with the 2-hydroxyethyl methacrylate
monomer and the initiator to the mixing device. Optionally, if the
mixing device has more than one port the 2-hydroxyethyl
methacrylate and initiator constituents may be added to the molten
polyolefin polymer.
In the method of the invention the feed rates of the constituents
to the melt mixing device is important. The 2-hydroxyethyl
methacrylate and initiator can be metered continuously or in
several portions over a period of time to promote homogeneous
grafting of the monomer throughout the mass of the polyolefin
polymer. Although not wishing to be bound by any theory it is
thought that the reaction is extremely fast and occurs to a major
extent when the 2-hydroxyethyl methacrylate and initiator come in
contact with the melt polyolefin polymer. However, the reaction may
continue while the molten polymer is being conveyed away from the
initial point of contact. The free radical initiator should be fed
to the melt blend at a rate relative to the feed rate of the
2-hydroxyethyl methacrylate, that is, the ratio of initiator feed
(weight basis) to monomer feed (weight basis) is greater than about
0.025, preferably, the free radical initiator relative feed rate is
from about 0.025 to about 0.1, more preferably, from about 0.025 to
about 0.075 and most preferably, from about 0.0375 to about
0.06.
Desirably, the 2-hydroxyethyl methacrylate monomer can be fed to
the melt blend at a rate relative to the feed rate of the
polyolefin, that is, the ratio of monomer (weight basis) to
polyolefin (weight basis) is from 0.05 to about 0.3, preferably the
monomer relative feed rate is from about 0.1 to about 0.25 and more
preferably, the relative feed rate is from about 0.1 to about 0.2.
Unexpectedly, it has been discovered that by adding the free
radical initiator and 2-hydroxyethyl methacrylate at the rates
described above the efficiency in grafting an amount of monomer to
the polyolefin is greater than about 50 percent.
The extruder can have more than one port for the addition of the
polyolefin polymer with one or more injection orifices at points
where the polyolefin is molten for addition of 2-hydroxethyl
methacrylate and/or the initiator. The extruder may also have a
section with a reduced pressure zone for venting off any unreacted
2-hydroxyethyl methacrylate and/or volatiles formed during the
process.
The grafted 2-hydroxyethyl methacrylate content of the final
modified polyolefin polymer can be from 5 weight percent to about
30 weight percent based on the total amount of monomer and
polyolefin resin fed. Desirably, the polyolefin, i.e. polyethylene
or polypropylene, has grafted thereto from 10 weight percent to
about 25 weight percent, and more preferably, from about 10 weight
percent to about 20 weight percent.
Although specific values have been stated for the ranges, one
skilled in the art would understand that such ranges implicitly
include all values within those ranges without specifically stating
such values herein.
The present invention is illustrated in greater detail by the
specific examples presented below, but it is to be understood that
these are illustrative embodiments and this invention is not to be
limited by any of the details of the description, but rather is to
be construed broadly within its scope and spirit.
For Examples 1-13 a linear regression calibration curve was derived
for each type of polyethylene following the methodology below.
Synthesis of Poly(2-hydroxyethyl methacrylate) Homopolymer
Five hundred and twenty (520) grams of ethyl acetate and 130 grams
of 2-hydroxyethyl methacrylate were added to a 1 liter,
three-necked flask. The flask was heated to 60-65.degree. C., while
stirring. The system was dosed and purged with nitrogen gas for one
hour. The system was opened and 1.12 grams of benzoyl peroxide was
added to the ethyl acetate/2-hydroxyethyl methacrylate solution.
The system was closed, again, with nitrogen gas purge. After
approximately four hours, a white precipitate had formed. The white
precipitate was removed from the flask, suction filtered to remove
excess solvent, and washed with 100-200 milliliters of ethyl
acetate. The white precipitate was dried in a vacuum oven at
50.degree. C. and 26 in Hg for ten hours to remove all solvent.
Calibration Curve for Determination of Percent Grafting Level by
FT-IR Analysis
Samples of predetermined weight ratios of the polyethylene and
synthesized poly(2-hydroxyethyl methacrylate) were blended in a
melt mixer. Thin films of these known blend compositions were
compression molded at a temperature of 374.degree. F. and a
pressure of 10,000-20,000 psi. Using FT-IR, the peak height ratio
for the band at 1725 cm.sup.-1 (due to the carbonyl group on
2-hydroxyethyl methacrylate) to the band at 720 cm.sup.-1 (due to
polyethylene) was determined for each of the
polyethylene/poly(2-hydroxyethyl methacrylate) blends. Using this
data, a graph of peak height ratio of 1725 cm.sup.-1 to 720
cm.sup.-1 versus percent poly(2-hydroxyethyl methacrylate) in the
blends was made. Using near regression, a best fit line was drawn
through the data.
The best fit linear regression equation for low density
polyethylene was:
% grafted HEMA=3.82+65.05 (Ratio of 1725 cm.sup.-1 to 720
cm.sup.-1).
The best fit linear regression equation for the linear low density
polyethylene was:
% grafted HEMA=-0.38+38.63 (Ratio of 1725 cm.sup.-1 to 720
cm.sup.-1).
EXAMPLES 1-4
A low density polyethylene polymer having a melt index of 1.9
dg/min (available from Dow Chemical Company, Midland, Mich.) was
grafted with 2-hydroxyethyl methacrylate by reactive extrusion.
This was a single-step continuous process in which the grafting
reaction was conducted in a 30 millimeter twin-screw extruder
(Wemer & Pfleiderer, ZSK-30) with vacuum devolatilization. The
extruder had a total processing length of 880 millimeters, nine
barrel sections and five heating zones. Barrel no. 1 was cooled by
water. The heating elements for barrels 2 and 3 were coupled as
Zone 1, barrels 4 and 5 were coupled as Zone 2, barrels 6 & 7
were coupled as Zone 3, barrel 9 was Zone 4 and the die was Zone 5.
Vacuum devolatilization was located approximate 700 millimeters
from the beginning of the screws. The polyethylene resin feed rate
was 22 lb/hr, the 2-hydroxyethyl methacrylate monomer feed rate was
2.2 lb/hr and the respective feed rate of the free radical
initiator is shown in Table 1 below. The constituent feed to the
extruder comprised contemporaneously adding, at the extruder feed
throat, the low density polyethylene resin, a solution of
2-hydroxyethyl methacrylate monomer (available from Aldrich
Chemical Company, Milwaukee, Wis.) and initiator
(2,5dimethyl-2,5di(t-butylperoxy) hexane, supplied by elf Atochem,
2000 Market St, Philadelphia, Pa. 19103-3222 under the tradename of
Lupersol 101). The screw speed of the extruder was 300 rpm. The
polymer melt was extruded into strands and cooled in a water bath
and subsequently pelletized by a strand-cut type pelletizer. The
collected pellets were dried under vacuum (29 inch Hg) for 18 hours
to remove water.
Purifying the modified polyolefin for determining crafted HEMA
content
To remove unreacted 2-hydroxyethyl methacrylate and any homopolymer
of 2-hydroxyethyl methacrylate the reaction products were purified.
To purify the modified polyolefin, 5 grams of the modified
polyolefin product obtained in the examples was added to a
round-bottom flask containing 125 milliliters of xylenes. The flask
was fitted with a condenser and stirred by a magnetic stirrer. The
contents were heated to 140.degree. C. to 150.degree. C. in an oil
bath and refluxed for 2 hours. After the modified polyolefin was
completely dissolved in the solution, the hot xylenes solution was
added, stirring continuously, to a beaker containing 800
milliliters of acetone at room temperature. The purified
precipitate was collected by vacuum filtration and washed with 100
milliliters of acetone. The purified precipitate was dried in a
vacuum oven at 50.degree. C. and 25-30 inches of Hg until all
solvent had been removed.
The purified products were pressed into a thin film at 374.degree.
F. and 10,000-20,000 psi and analyzed by Fourier-Transform Infrared
Spectroscopy (FT-IR). The FT-IR spectra were collected using an
Impact 400 model infrared spectrometer manufactured by Nicolet
Instrument Corporation (5225 Verona Road, P. O. Box 44451, Madison,
Wis. 53744-4451). In order to determine the degree of grafting of
2-hydroxyethyl methacrylate onto the particular polyethylene for a
particular extrusion product, the peak height ratio for the band at
1725 cm.sup.-1 (due to the carbonyl group on 2-hydroxyethyl
methacrylate) to the band at 720 cm.sup.-1 (due to polyethylene)
was determined for each of the purified products. The calibration
curve equation described above was used to convert this peak height
ratio into the weight percent of grafted 2-hydroxyethyl
methacrylate in each sample. The grafting level and grafting
efficiency results appear in Table 1 below. The percentages are
weight percent based on the weight of the polyethylene and grafted
2-hydroxyethyl methacrylate. A general discussion of using FT-IR
for determining grafting efficiency is in "Melt grafting of
t-butylaminoethyl methacrylate on polyethylene" by Song and Baker,
POLYMER, Volume 33, Number 15 (1992), the disclosure of which is
incorporated herein by reference.
TABLE 1 Ex. No. Zone Temps. .degree. C. Initiator rate lb/hr FT-IR
ratio % Grafted Graft Eff. % 1 159, 175, 183, 173, 181 0.022 0.0188
5.0 50 2 160, 180, 187, 177, 181 0.044 0.0438 6.6 66 3 161, 180,
188, 178, 181 0.066 0.0770 8.7 87 4 166, 180, 189, 178, 181 0.088
0.0561 7.3 73
EXAMPLES 5-13
For examples 5-13, a linear low density polyethylene having a melt
index of 1.9 dg/min and a density of 0.917 g/cc (supplied by Dow
Chemical Company, Midland, Mich.) was 5 fed to a Haake twin screw
extruder (available from Haake, 53 West Century Road, Paramus,
N.J., 07652). The extruder was 300 millimeters long having counter
rotating twin conical screws. Each conical screw was 30 millimeters
at the feed port and 20 millimeters at the die. The extruder had 4
temperature zones with the die being designated as Zone 4. The
temperature of each zone is shown in Table 2. The constituent feed
to the extruder comprised contemporaneously adding, at the extruder
feed throat, the linear low density polyethylene resin at a rate of
5 lb/hr, the feed rates of the 2-hydroxyethyl methacrylate and the
initiator (Lupersol 101) for each example are:
Example 5, the feed rate of the 2-hydroxyethyl methacrylate was
0.25 lb/hr, the feed rate of the initiator was 0.017 lb/hr and the
screw speed was 150 rpm.
Example 6, the feed rate of the 2-hydroxyethyl methacrylate was
0.50 lb/hr, the feed rate of the initiator was 0.025 lb/hr and the
screw speed was 150 rpm.
Example 7, the feed rate of the 2-hydroxyethyl methacrylate was
0.75 lb/hr, the feed rate of the initiator was 0.030 lb/hr and the
screw speed was 150 rpm.
Example 8, the feed rate of the 2-hydroxyethyl methacrylate was 1.0
lb/hr, the feed rate of the initiator was 0.038 lb/hr and the screw
speed was 150 rpm.
Example 9, the feed rate of the 2-hydroxyethyl methacrylate was
0.50 lb/hr, the feed rate of the initiator was 0.025 lb/hr and the
screw speed was 50 rpm.
Example 10, the feed rate of the 2-hydroxyethyl methacrylate was
0.50 lb/hr, the feed rate of the initiator was 0.025 lb/hr and the
screw speed was 100 rpm.
Example 11, the feed rate of the 2-hydroxyethyl methacrylate was
0.50 lb/hr, the feed rate of the initiator was 0.025 lb/hr and the
screw speed was 200 rpm.
Example 12, the feed rate of the 2-hydroxyethyl methacrylate was
0.50 lb/hr, the feed rate of the initiator was 0.025 lb/hr and the
screw speed was 150 rpm.
Example 13, the feed rate of the 2-hydroxyethyl methacrylate was
0.50 lb/hr, the feed rate of the initiator was 0.025 lb/hr and the
screw speed was 150 rpm.
Following the procedures of Examples 1-4, each reactant product was
purified, pressed into a film and tested using FT-IR analysis to
determine the weight percent of 2-hydroxyethyl methacrylate grafted
onto the LLDPE. Using the linear regression calibration curve for
linear low density polyethylene, the amount of 2-hydroxyethyl
methacrylate grafted to the of linear low density polyethylene was
determined. The grafting level and grafting efficiency results
appear in Table 2 below.
TABLE 2 Wt. % Graft Ex. No. Zone Temps. .degree.C. FT-IR ratio
Grafted Eff. 5 180, 200, 200, 200 0.0723 2.4 49 6 180, 200, 200,
200 0.208 7.7 77 7 180, 200, 200, 200 0.387 14.6 97 8 180, 200,
200, 200 0.527 20 100 9 180, 200, 200, 200 0.0171 0.3 3 10 180,
200, 200, 200 0.151 5.5 55 11 180, 200, 200, 200 0.228 8.4 84 12
170, 180, 180, 180 0.273 10 100 13 180, 210, 210, 210 0.231 8.5
85
COMPARATIVE EXAMPLE A
Polypropylene polymer having a melt flow index of 35 dg/min
(available from Montell, Three Little Falls Center, 2801
Centerville Rd., Wilmington, Del.) was fed to the Haake twin screw
extruder at a feed rate of 5.0 lb/hr. Using gel permeation
chromatography analysis (GPC), the polypropylene was determined to
have a number average molecular weight (M.sub.n) of 60,100 g/mol, a
weight average molecular weight (M.sub.w) of 166,800 g/mol, and a
polydispersity (M.sub.w /M.sub.n) of 2.78. The screw speed was set
at 150 rpm and the four zone temperatures were set at 170, 180,
180, 180.degree. C.
COMPARATIVE EXAMPLE B
Following the procedure of Comparative Example A the polypropylene
was extruded at a peroxide initiator rate of 0.026 lb/hr. By GPC
analysis, the M.sub.n was determined to be 40,900 g/mol, the
M.sub.w was 90,700 g/mol and a polydispersity of 2.22. These values
show that the addition of the free radical initiator produces
severe degradation of the polypropylene.
EXAMPLES 14-20
The polypropylene of Comparative Example A was extruded using the
Haake extruder (describe Examples 5-13). The screw speed was set at
150 rpm and the four zone temperatures set at 170.degree. C.,
180.degree. C., 180.degree. C. and 180.degree. C. The polypropylene
resin, 2-hydroxyethyl methacrylate and initiator feed rates, in
lb/hr., are in Table 3 below.
TABLE 3 EXAMPLE PP resin HEMA Initiator 14 4.7 0.49 0.014 15 4.8
0.49 0.025 16 4.8 0.49 0.048 17 5.0 0.52 0.026 18 4.8 0.96 0.025 19
9.0 0.96 0.07 20 10.3 0.96 0.065
Following the procedures of Examples 1-4, each reactant product was
purified and analyzed for elemental oxygen content by weight
percent The weight percent of oxygen in each sample was then
divided by the weight fraction of oxygen in 2-hydroxyethyl
methacrylate (0.369), to determine the weight percent of grafted
2-hydroxyethyl methacrylate in each sample. The grafting level and
grafting efficiency results appear in Table 4 below. The elemental
oxygen content of each sample was determined by Galbraith
Laboratories, Inc. Knoxville, Tenn.
TABLE 4 Ex. No. Wt. % Grafted Graft Efficiency 14 1.9 18 15 5.6 55
16 5.9 58 *17 6.2 59 18 10.6 53 19 4.3 40 20 3.1 33 *This modified
polypropylene was determined by GPC to have an M.sub.n of 55,300
g/mol, an M.sub.w of 146,900 g/mol and a polydispersity of 2.66.
This indicates that the grafting of 2-hydroxyethyl methacrylate
onto polypropylene using the process of the invention did not
result in substantial degradation of the polypropylene.
EXAMPLE 21
The polypropylene of Comparative Example A was extruded using the
30 millimeter twin-screw extruder (Werner & Pfleiderer, ZSK-30)
with vacuum devolatilization similar to that described above for
Examples 14 with the following exception. The extruder had a total
processing length of 1228 millimeters. Unreacted monomer was
removed by vacuum devolatilization at the end of the extruder. The
polypropylene resin feed rate was 25 lb/hr, the 2-hydroxyethyl
methacrylate monomer feed rate was 2.25 lb/hr and the initiator
feed rate was 0.125 lb/hr. The screw speed was 300 rpm and all the
barrels temperatures were set at 190.degree. C. The constituent
feed to the extruder comprised injecting 2-hydroxyethyl
methacrylate monomer into an injection port at a point where the
polypropylene was melted. The initiator was injected into the melt
blend at a subsequent injection port. The resulting polymer strands
were cooled in a water bath, pelletized and dried under 29 inches
of Hg vacuum for 18 hours to remove the water. The weight percent
of grafted 2-hydroxyethyl methacrylate, determined by elemental
oxygen content, was 2.57.
While the invention has been described with reference to a
preferred embodiment, those skilled in the art will appreciate that
various substitutions, omissions, changes and modifications may be
made without departing from the spirit hereof. Accordingly, it is
intended that the foregoing examples be deemed merely exemplary of
the present invention and not be deemed a limitation thereof.
* * * * *